The present invention relates to a thin-film semiconductor element, a thin-film semiconductor device, and methods of fabricating the element and device, and more particularly to a thin-film semiconductor element and a thin-film semiconductor device which are used for the driving device of a liquid crystal display device or the like, and to methods of fabricating the element and device.
A thin-film transistor (hereinafter referred to as "TFT") formed on an insulating substrate such as a glass substrate has hitherto been applied to a liquid crystal flat panel display device of the active matrix type and a line image sensor for facsimile, and the improvement of the TFT has been promoted in various fields. A TFT using amorphous silicon is now widely used to form the liquid crystal display device and the line images sensor, since the above TFT having a large area can be readily produced at low temperatures.
Examples of the technology concerning a TFT have been described in Japanese Patent Applications JP-A-63-9,157 and JP-A-1-302,769. The above-referred patent application JP-A-63-9,157 discloses a method of fabricating a TFT. According to the invention disclosed in this patent application, the number of etching steps is reduced, so that the quality of the fabricated TFT is improved, and a step of positioning source and drain electrodes which are to be accurately located, is omitted. Further, the patent application JP-A-1-302,769 discloses a method of fabricating a TFT. According to the invention disclosed in this patent application, a gate electrode and a gate insulating film are successively formed on a substrate by the well-known method. Further, an intrinsic semiconductor film and an n-type semiconductor film are successively formed on the gate insulating film by the CVD method, source and drain electrodes are formed on the n-type semiconductor film so that the source electrode and the drain electrode are separated from each other. Then, that region of the n-type semiconductor film which corresponds to a gap between the source electrode and the drain electrode, is doped with a p-type impurity, to make this region intrinsic. It is noted that the n-type semiconductor film is formed by the CVD method.